Method for monitoring an internal combustion engine

ABSTRACT

A method for monitoring an internal combustion engine is described in which fuel is injected directly into at least one combustion chamber in at least two partial injections via at least one final controlling element, in which an actual torque is determined at least on the basis of one fuel mass that is to be injected and/or has been injected, such actual torque being compared with a permitted torque of the internal combustion engine and an error response being initiated if the actual torque is in a predefined ratio to the permitted torque. A corresponding application of the method for monitoring an internal combustion engine as well as a corresponding device are also described.

FIELD OF THE INVENTION

The invention relates to a method for monitoring an internal combustionengine in which fuel is injected directly into at least one combustionchamber in at least two partial amounts via at least one finalcontrolling element, in which, at least on the basis of a fuel massinjected and/or to be injected, an actual torque of the internalcombustion engine is determined, such actual torque then being comparedwith a permissible torque of the internal combustion engine, and anerror response being initiated when the actual torque is in a predefinedratio to the permissible torque.

The invention further relates to a corresponding application of themethod for monitoring an internal combustion engine as well as acorresponding device.

DESCRIPTION OF RELATED ART

Modern internal combustion engines are equipped with engine controllerswhich control the power output and torque of the internal combustionengine by regulating particular parameters as a function of inputvariables. Multiple monitoring measures to ensure the safe operation andthe availability of the internal combustion engine must be provided toprevent malfunctions, in particular malfunctions of the electroniccontrol unit for the engine controller.

DE 199 00 740 [[A1]] introduces a method and a device for operating aninternal combustion engine which is operated using a lean air/fuel blendunder certain operating conditions. The fuel mass to be injected, and/orthe injection time to be used is determined on the basis of a setpointvalue. In order to monitor operability, the actual torque of theinternal combustion engine is determined on the basis of the fuel massto be injected and/or the injection time which has been or is to bedetermined, compared with a maximum permissible torque, and an errorresponse is initiated if the actual torque exceeds the maximumpermissible torque. According to DE 199 00 740 A1, the fuel mass to beinjected is determined on the basis of the injection time, which istransmitted from the controller, and possibly additional variables suchas the fuel pressure. The fuel mass thus determined is converted to atransmitted engine torque which is corrected taking into accountefficiencies such as, for example, the injection time efficiency. At thesame time, a variable representing the oxygen concentration in theexhaust gas is compared with at least one predefined threshold value andan error response is initiated if it exceeds the threshold value.

DE 101 23 035.4 (not a prior publication) discloses an internalcombustion engine in which fuel metering may be divided into at leastone first partial injection and a second partial injection. During thesecond partial injection, a fuel quantity variable, which characterizesthe fuel quantity that is injected during the second partial injection,is corrected on the basis of at least one pressure variable, whichcharacterizes the fuel pressure, the fuel quantity variable, and atleast one additional variable.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a method formonitoring the torque of an internal combustion engine according towhich fuel metering is divided into at least one first partial injectionand a second partial injection.

The object is achieved by a method for monitoring an internal combustionengine in which fuel is injected directly into at least one combustionchamber in at least two partial injections via at least one finalcontrolling element, in which an actual torque of the internalcombustion engine is determined at least on the basis of a fuel massinjected and/or to be injected, such actual torque is then compared witha permissible torque of the internal combustion engine, and an errorresponse is initiated if the actual torque is in a predefined ratio tothe permissible torque, and in which a total fuel volume of all partialinjections is taken into account for the determination of the fuel massthat has been and/or is to be injected.

This measure according to the present invention provides a highlyadvantageous method for torque monitoring which takes into accountmultiple partial injections and may be applied in any operatingsituation.

A fuel volume of a partial injection is advantageously determined atleast on the basis of an actuation period of the final controllingelement in question and a pressure acting on the fuel. A variabledefining the actuation start may be considered instead of or in additionto such pressure. This may be performed, for example, via acharacteristic map that is stored in the control device of the internalcombustion engine and applied specifically to the partial injection towhich it relates. If the final controlling element is designed as aninjector, the corresponding fuel volume value is derived from thecharacteristic map on the basis of input variables including theactuation time of the injector in question and the pressure acting onthe fuel (in common rail internal combustion engines, this is the railpressure in the common rail). If the final controlling elementconfigured as a unit injector system or a unit pump system, theactuation start is used instead of the pressure.

The total fuel volume of a combustion cycle may then be determined fromthe sum total of the fuel volume of all partial injections. Based onthis total fuel volume, a fuel mass may be determined via a known fueldensity.

An advantageous refinement of the present invention provides that thedetermined fuel volume of a partial injection is corrected depending onan actuation start of the injector in question. Such correction isadvantageously done using a correction factor that is derived from aninjection efficiency characteristic map which is a function of theactuation start. This refinement offers the great advantage ofconsidering the possibly non-linear correlation between the actuationstart of the injector and the attained torque effect achieved. In viewof the current state of development of modern internal combustionengines having exhaust aftertreatment systems this is a beneficialapproach, for in such engines a modified actuation start does notnecessarily influence the torque generated by the internal combustionengine but may merely cause a rise in the temperature of the exhaustgas.

According to a particularly advantageous refinement of the presentinvention, the previously determined fuel mass is linked to a wavecorrection mass to yield a corrected fuel mass. This may be achieved,for example, by subtracting the wave correction mass from the previouslymeasured fuel mass. This correction provides a highly advantageousmethod for taking into account wave phenomena that might occur in a highpressure injection system such as a common rail system, in the feed linefrom the fuel reservoir to the injector, and influence the fuel massinjected during the injector actuation time. The wave correction mass isadvantageously determined on the basis of at least the fuel volume ofthe partial injections and the pressure acting on the fuel.

A torque of the internal combustion engine is determined from the fuelmass that has been corrected in the manner described above together witha rotational speed of the internal combustion engine. This isadvantageously performed via a characteristic map that is stored in theengine controller. It is also possible to include other influencingparameters besides the rotational speed of the internal combustionengine. According to the present invention, the determined torque of theinternal combustion engine is linked to an efficiency correction factorto produce a corrected torque of the internal combustion engine. Thisefficiency correction factor particularly advantageously considersinfluencing parameters such as the temperature of the internalcombustion engine, engine friction, oil temperature and oil quality.

The error response is then advantageously initiated if the actual torqueis greater than the permissible torque.

A further advantage is provided by the use of the monitoring methodaccording to the present invention for monitoring a direct injectiondiesel engine, in particular one having a common-rail system and/or aunit injector system or a unit pump system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a first exemplary embodiment of the method according to thepresent invention.

FIG. 2 shows a detail of the first exemplary embodiment.

FIG. 3 shows a possible extension of the first exemplary embodiment.

FIG. 4 shows a second exemplary embodiment of the method according tothe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a first exemplary embodiment of the method according to thepresent invention for monitoring an internal combustion engine. Theobject of the method described in FIG. 1 is to determine an actualtorque, which is compared with a permissible torque. The methoddescribed in FIG. 1, which normally runs in the engine controller of aninternal combustion engine, assumes that certain input variables havebeen previously stored in the engine controller. These input variablesare identified in FIG. 1 by reference numbers 1 through 7, 17, 22 and24.

The exemplary embodiment represented in FIG. 1 is described on the basisof various injection modes, such as are normally used in directinjection diesel engines. However, the method according to the presentinvention is not limited to diesel engines; it can be applied inprinciple to any direct injection internal combustion engine havingmultiple injection modes.

The direct injection diesel engine that is monitored by the methodaccording to FIG. 1 is a common rail diesel engine in which the fuel forinjections is available in a shared fuel distributor, the common rail.From the common rail, where the fuel is under high pressure, the fueltravels through normally short, high-pressure feed lines to theinjectors, which inject the fuel directly into the combustion chambersof the engine. The pressurized fuel available in the common rail allowsvarious fuel injection modes to be used for injecting fuel into the samecombustion chamber. These various injection modes may be pilotinjection, main injection, or post-injection.

Reference number 1 in the method described in FIG. 1 refers toinstantaneous rail pressure p. Reference number 2 refers to theactuation period of an injector for a main injection ti_Main. This maininjection generates most of the torque of the internal combustionengine. Reference number 3 refers to the actuation period of theinjector for a first pilot injection ti_Pilot1. This first pilotinjection may be initiated, for example, when the crankshaft is at anangle 10 to 20 degrees prior to the main injection and its main effectbesides generating torque is to reduce the running noise of the engine.Reference number 4 refers to the actuation period of a second pilotinjection ti_Pilot2. This second pilot injection may help reduce therunning noise of the internal combustion engine but in conjunction withthe first pilot injection, for example may also improve exhaust gasvalues. Reference number 5 refers to a third pilot injection ti_Pilot3,for example, which may be injected into the combustion chamber wellbefore any of the other injections, thereby significantly increasingtorque. Reference number 6 refers to the actuation time of the injectorfor a first post-injection ti_Post1, and reference number 7 refers tothe injector actuation time of a second post-injection ti_Post2. Bothpost-injections are primarily used to lower exhaust emissions andpossibly to clean an N_(ox) accumulator-type catalytic converter orparticle filter.

Rail pressure p according to reference number 1 and the injectoractuation time for main injection ti_Main, referred to by referencenumber 2, are supplied to a characteristic map Main (reference number8). Depending on the actuation time supplied and the rail pressure p,the output from characteristic map Main (reference number 8) is a fuelvolume of the main injection, which is supplied to a summer 14. Theinstantaneous rail pressure p, referred to by reference number 1, andthe corresponding injector actuation times expressed as referencenumbers 3 (ti_Pilot1), 4 (ti_Pilot2), 5 (ti_Pilot3), 6 (ti_Post1) and 7(ti_Post2) are supplied to the characteristic maps Pilot1 (referencenumber 9), Pilot2 (reference number 10), Pilot3 (reference number 11),Post1 (reference number 12), and Post2 (reference number 13). The resultis a fuel volume in each case, similar to the characteristic map 8,which is also supplied to summer 14. At point 15, summer 14 provides, asa result, the total fuel volume introduced into a combustion chamberthroughout a combustion cycle via the injector using various injectionmodes.

This fuel volume is then supplied to a node 16, which also receives thesignal regarding fuel density rho from signal block 17. The linkage,i.e., multiplication of the fuel volume by fuel density rho 17 yieldsfuel mass 18.

Fuel mass 18 is supplied to a subtractor 19, which has the output signalfrom a signal block 20 as a further input signal. A wave correction fuelmass is determined in signal block 20 and is used to compensate forwaves arising in the high pressure line between the common rail and theassociated injector, which occur when multiple injection modes areexecuted in rapid succession. When several injections are executed inrapid succession, the fuel in the high pressure line may not have fullysettled by the time the next injection occurs. This condition causes thephysical phenomenon of a standing wave in the high-pressure line. Theinput variables applied to wave correction according to block 20 areinstantaneous rail pressure p from block 1, fuel density rho from block17, and the output signals from characteristic maps 8, 9 and 10, on thebasis of which the fuel volumes for the main injection as well as thefirst and second post-injections are supplied to wave correction block20. The way in which the wave correction fuel mass is determined inblock 20 will be described in the explanation of FIG. 2 below.

As indicated previously, the output signal from wave correction block 20is supplied to subtractor 19. The subtractor subtracts the wavecorrection fuel mass from the previously determined fuel mass 18. Theresulting corrected fuel mass is supplied to a torque characteristic map21. Torque characteristic map 21 also receives rotational speed n of theinternal combustion engine from block 22. The output variable from thesupplied corrected fuel mass and rotational speed n is the torque of theinternal combustion engine.

This determined torque of the internal combustion engine is supplied tonode 23. Node 23 also receives the signal from block 24. The signal fromblock 24 is an efficiency factor that is present in the enginecontroller. This efficiency factor takes into account certain variablesincluding the temperature of the engine, the engine friction, the oiltemperature, the oil quality and, where applicable, other influencingparameters. Efficiency factor 24 is multiplied by the previouslydetermined torque of the internal combustion engine in node 23. Theoutput from node 23 is the calculated actual internal torque of theinternal combustion engine.

This actual torque 25 is supplied to a comparison routine 26, in whichthe previously determined actual internal torque is compared with amaximum permitted internal torque of the internal combustion engine. Ifit is determined that the actual internal torque is greater than thepermitted torque of the internal combustion engine, an error response isinitiated. Such an error response might be, for example, a safetycut-off of the fuel supply or limiting the rotational speed of theinternal combustion engine. Limiting the rotational speed is preferredto possibly limiting the torque because the rotational speed is easierto monitor. Other error responses might include making an entry in anerror log, displaying an error message to the operator of the vehicle orre-starting the engine controller.

Determining permitted torque is known to those skilled in the art andmay be calculated, for example, according to the monitor concept via aredundant torque path in the engine controller. One of the variablesinfluencing the permitted torque is, for example, the operation of thegas pedal.

FIG. 2 shows in detail wave correction block 20, as was shown previouslyin the description of FIG. 1. As was indicated in the description ofFIG. 1, the fuel volume of first pilot injection Pilot1 (referencenumber 30), the fuel volume of second pilot injection Pilot2 (referencenumber 31), instantaneous rail pressure p (reference number 32), thefuel volume of main injection Main (reference number 33) and density rhoof the fuel used (reference number 17) are supplied to the wavecorrection block as inputs. From the supplied fuel volumes (30, 31 and33) and supplied fuel density rho (17), the wave correction block firstdetermines the pertinent fuel mass in signal blocks 30, 31 and 33, thatfuel mass then being available as an output signal from each of blocks30, 31 and 33. FIG. 2 does not show the associated linkages with fueldensity rho since there is an option to supply the determined fuelmasses directly to the wave correction block. With reference to thedrawing in FIG. 1, this procedure would require that after eachindividual fuel volume has been determined, it be converted toindividual fuel masses before the individual fuel masses are combined ina summer (corresponds to block 14 in FIG. 1) to yield a total fuel mass.In this case, each individual fuel mass would immediately be availableas a signal. The final decision on which method to use will depend onthe selection of those skilled in the art based on various influencingparameters, such as the runtime values of the controller.

Instantaneous rail pressure 32 and the fuel mass of main injection 33are supplied to a first quantity correction characteristic map 34 asinput variables. The result from quantity correction characteristic map34 is a first corrected quantity 35. The same input variables as weresupplied to quantity correction characteristic map 34 are also suppliedas inputs to a quantity correction characteristic map 36. The resultfrom second quantity correction characteristic map 36 is a secondcorrected quantity 37. The fuel mass of main injection 33 and the fuelmass of first pilot injection 30 are supplied as input variables to athird quantity correction characteristic map 38. The result from thisthird quantity correction characteristic map is a third correctedquantity 39. First corrected quantity 35 and second corrected quantity37 are supplied to a first selector block 40. Third corrected quantity39 is supplied to a second selector block 41. Second selector block 41also receives a preset factor 42 as an input variable, which in thisembodiment is set to zero. In other words, the output variable fromfirst selector block 1 is either first corrected quantity 35 or secondcorrected quantity 37, and the output value from second selector block41 is either third corrected quantity 39 or preset value 42 (=0).

The fuel mass of second pilot injection 31 is supplied to a first inputof a first query logic circuit 43, which then returns a “High Level” asthe output value when the first input value received by query logiccircuit 43 is greater than the second input value. A second preset value44, zero in this exemplary embodiment, is supplied to first query logiccircuit 43 as a second input value. First query logic circuit 43functions in such a way that the result of query logic circuit 43indicates “High Level” if fuel mass variable 31 is present. If the valuefor fuel mass 31 is absent, the output value from query logic circuit 43is “Low Level”.

The fuel mass of first pilot injection 30 is supplied to a first inputof a second query logic circuit 49, which then returns a “High Level” asthe output value when the first input value received by query logiccircuit 49 is greater than the second input value. A fourth preset value50, which is set to zero in this embodiment, is supplied to second querylogic circuit 49 as a second input value. Second query logic circuit 49functions in such a way that the result of query logic circuit 49indicates a “High Level” if fuel mass value 30 is present. If the valuefor fuel mass 30 is absent, the output value from query logic circuit 49is “Low Level.”

The output signal from first query logic circuit 43 is supplied to a NOTgate 45. The output value from NOT gate 45 is supplied to a gate inputof first selector gate 40. When first selector gate 40 is in a neutralposition (for a “Low Level” signal at the gate input), it sends a signalof first correction quantity to block 35 as the output value from firstselector gate 40. On the other hand, if a “High Level” is at the gateinput, second corrected quantity 37 is output as the output variablefrom first selector gate 40. The output value from first selector gate40 is supplied to a summer 46.

The output signal from second query logic circuit 49 is supplied to aninput gate of second selector gate 41. When second selector gate 41 isin a neutral position (for a “Low Level” signal at the gate input), itsends a signal of first preset value (in this case zero) to block 42 asthe output value from second selector gate 41. On the other hand, if a“High Level” is at the gate input, third corrected quantity 39 is outputas the output variable from second selector block 41. The output valuefrom second selector gate 41 is also supplied to summer 46.

The output signals from query logic circuits 43 and 49 are also suppliedto an OR gate 51, which has “High Level” as the output signal if anoutput signal from query logic circuits 43 and 49 also indicate “HighSignal”. If only “Low Signals” are present at the input of OR gate 51,the output of OR gate 51 will also return only a “Low Signal.”

The output signal from summer 46 is supplied to a third selector block47, which also receives a third preset value 48 as an additional inputvalue, set to zero in this embodiment. The output signal from OR gate 51is supplied to the input of third selector block 47. When third selectorgate 47 is in a neutral position (for a “Low Level” signal at the gateinput), it returns the signal of the third preset value (i.e. zero) toblock 48 as the output value from third selector gate 47. On the otherhand, if a “High Level” is at the gate input, the output value fromsummer 46 is output as the output variable from third selector block 47.

The output signal from third selector block 47 is supplied to an outputsignal block 52 and represents the desired wave correction quantity thatis used in the configuration according to FIG. 1.

FIG. 3 shows a possible extension of the first embodiment in FIG. 1. Inmodern diesel engines equipped with exhaust aftertreatment systems, itmay happen that the injector actuation period and in particular theactuation start may be modified so that they do not affect the torque.Theoretically, this condition may occur during all injection modesdescribed earlier. In such cases, the start and duration of fuelinjection actuation do not return an unequivocal analysis of thegenerated torques. For example, it is possible to retard the actuationstart of the main injection from a few degrees before top dead center toa few degrees after top dead center to regenerate an exhaustaftertreatment system. This delay of the injection start does not affectthe torque and results merely in an elevated combustion temperaturewhich assists in the regeneration of the exhaust aftertreatment system.In these instances it is thus necessary to consider the effectiveness ofthe actuation start and duration. This is accomplished by the methoddescribed in the embodiment in FIG. 3. Actuation start 60 is supplied toan effectiveness characteristic map 61. This effectivenesscharacteristic map 61 must be stored individually for each injectionmode in the engine controller. The output value from the effectivenesscharacteristic map is a correction factor 62 which enables thedetermined fuel volumes as output variables of blocks 8, 9, 10, 12 and13 according to FIG. 1 to be corrected. For example, it might bepossible to extend the main injection by factor 2 while retarding theactuation start, as described earlier, from a few degrees before TDC toa few degrees after TDC. This modification to the main injection wouldhave no impact on the torques which would necessitate the use of thecorrection factor 0.5, since the doubled fuel volume only results in thesame torque. Also, an additional effectiveness characteristic map may beused for the injection duration, or a combined effectivenesscharacteristic map for the injection start and duration might be used.

A further refinement of the method according to the present inventionprovides for a plausibility check of the fuel mass determined as shownin the exemplary embodiment of FIG. 1. This may be assured, for example,by combining a lambda sensor value with the signal from a hot film airmass flow meter and the rotational speed while measuring the exhaustfeedback rate. In this way, a second, independent fuel mass variable canbe determined. This in turn enables the mass of fuel actually injectedto be calculated precisely within reasonable tolerances, therebyproviding an average injected fuel mass derived from independentvariables which may be used in a plausibility check of the fuel massderived from the actuation data.

In summary, the monitoring method according to the present inventionprovides a capability for continuous monitoring of torques throughoutthe entire speed range of the internal combustion engine. This increasesthe safety of the overall system and assures improved error response.

In the context of this application, the comparison of torques wasdescribed on the basis of internal torques of the internal combustionengine. Nevertheless, the invention may be used for any given torqueprovided the torques are comparable.

The input data according to FIG. 1 is advantageously determinedsynchronously with the rotational speed. This measurement is carried outby the controller (not shown in the figures) of the internal combustionengine which is not included in the scope of this application.

The device according to the present invention is an internal combustionengine having a controller capable of performing the method according tothe present invention.

Besides the common rail systems, in which pressure buildup is initiatedby the controller and, at the end of fuel metering, separated therefromother systems are also known in which pressure buildup and the controlof fuel metering are closely linked. These systems also requiremonitoring of the control unit such as is provided by the presentinvention. This applies in particular to the unit injector systemsand/or unit pump systems. In general, the method described herein may beused for all fuel metering systems in which the start and end of fuelmetering are modified via a final controlling element. The actuationstart of this final controlling element generally determines the startof fuel metering, and the actuation end is defined by the end of fuelmetering. The period between the actuation start and finish is againdefined by the quantity of fuel to be injected.

Normally, the unit injector systems carry out only one main injection,one pilot injection and one post-injection. In theory, additionalinjections are also possible. In the following, this method will bedescribed with reference to the example of the first pilot injection andthe second post-injection. According to the present invention, thisprocedure may be applied to the other injection modes and/or to more orfewer partial injections.

In the method described in the foregoing, with a common rail system, theessential influencing parameters are the fuel amount to be injected, theactuation time and the rail pressure. These variables are considered viathe corresponding characteristic maps. Additional variables may also betaken into account, such as for example, rotational speed, fuel density,and/or temperature variations. In contrast to the foregoing, the presentinvention recognized that in a unit injector system, or a unit pumpsystem, or generally in a system in which the pressure buildup is notdecoupled from the fuel metering, the essential influencing variables onthe fuel quantity are the actuation start and duration. The rotationalspeed, temperature, and/or the fuel density may also be taken intoaccount in addition to these variables. Other variables thatcharacterize the actuation start may also be used instead of theactuation start. In particular, a feed start signal may be used.

Using these variables, a default fuel mass QKV, also known as thevirtual fuel mass, is set. Using this virtual fuel mass QKV as areference, the actual torque is determined by torque characteristic map21 as shown in FIG. 1 and the plausibility check is performed on thatbasis.

The method is described in greater detail in FIG. 4. Elements that weredescribed in the earlier figures are designated with the same referencenumbers. Besides rotational speed 22, the actuation time for the maininjection ti-Main, for the first pilot injection ti_Pilot1, and for thesecond post-injection ti_Post2, the corresponding actuation starts arealso required.

Actuation start FB_Main for the main injection has reference number 3B.This variable is supplied to a first mass calculation unit 200 togetherwith rotational speed N and the actuation time ti_Main of the maininjection.

Actuation start FB_Pilot1 for the first pilot injection has referencenumber 7B. Actuation start FB_Pilot1, actuation time ti_Pilot1 of thefirst pilot injection and the engine speed are supplied to a second masscalculation unit 210.

Actuation start FB_Post2 of a second post-injection has reference number2B and is supplied to a third mass calculation unit 220 together withactuation time ti_Post2 and a rotational speed N.

The first, second, and third mass calculation units store the fuel massof the corresponding partial injections, depending on the rotationalspeed, actuation time and the associated actuation start. In a simpledesign, a three-dimensional characteristic map is provided for thispurpose. Such a three-dimensional characteristic map may be implementedfor example via several two-dimensional characteristic maps or curves.In one embodiment, it is further possible to provide that thecalculation be made via appropriate functions instead of acharacteristic map, based on the described input variables. In thiscase, the characteristic map may be advantageously approximated with annth degree polynomial.

The output signal from second mass calculation unit 210 is supplied bothto a first mass correction unit 215 and to a node 217. Similarly, theoutput signal from the third mass calculation unit is passed to a secondmass correction unit 225 and a second node 227. The first and secondmass correction units, 215 and 225 respectively, each store a correctionfactor which is used to correct the output variable from the second masscalculation unit and the third mass calculation unit respectively insuch a way that the mass signals incident at each of nodes 217, and 227correspond to the fuel mass that will deliver a contribution to thetorque. This is necessary because the fuel quantities during pilotinjection and post-injection have less effect than those of the maininjection. Consequently, larger fuel amounts must be injected during thepre- and post-injections than during main injection in order to achievethe same torque. This effect is taken into account by mass correctionunits 215 and 225.

It is further possible to provide for the injection of additional fuelfor the exhaust aftertreatment system. This fuel may be used tocondition the exhaust aftertreatment system, such as a particle filter,and/or an oxidation catalytic converter. This fuel mass is calculated byexhaust gas correction unit 235.

The individual output signals from first mass calculation unit 200, thenode 217, node 227 and possibly exhaust gas correction unit 225 aretotaled in nodes 218, 228 and 238. This means that there is a virtualfuel mass available at output from node 238 that corresponds to the fuelmass which should have been apportioned in the main injection to producea given torque.

In node 248, the output signal from node 238 is combined with outputsignal TK from temperature correction unit 240. A signal fromtemperature sensor 242 is supplied to temperature correction unit 240.Other signals, such as rotational speed N, may be considered in additionto this signal. Based on the temperature, a factor is determined whichtakes into account the effect of the fuel temperature on the fuel mass.

As an alternative to the described method, the individual output signalsfrom the mass calculation units may be corrected accordingly. It ispossible to use multiple correction factors for the various partialinjections.

The virtual fuel mass signal after temperature correction is thentransmitted to torque characteristic map 21, as shown in FIG. 1. Thismethod presents an advantage since there are certain systems in whichpressure buildup is not decoupled from fuel metering, and the injectedfuel amount depends primarily on the injection actuation start angle.This dependency is not the case in common rail systems. In thesesystems, only the torque that is produced by a given quantity of fuel isdependent on the actuation start. In this case, the fuel mass depends onthe actuation start to a much greater degree than in coupled systems.

In the method described in FIG. 1, the fuel temperature is included inthe calculation of the fuel mass, based on the volume. This is normallytaken into account via the fuel density. In unit injector systems, orcoupled systems, the fuel temperature has a much greater influence andas such is taken into account via a separate correction factor.

The particular advantage of this method is that the characteristic mapsused are often also used to control the fuel injection.

1. A method for monitoring an internal combustion engine, in which fuelis injected directly into at least one combustion chamber in at leasttwo partial injections, using at least one final controlling element,comprising determining an actual torque of the internal combustionengine based on at least one injected fuel mass or one fuel mass to beinjected, comparing this actual torque to a permitted torque of theinternal combustion engine, and initiating an error response if theactual torque is at a predefined ratio to the permitted torque, wherein:for each partial injection, a fuel volume acting to generate a torque isdetermined; a total fuel volume of a combustion cycle is ascertainedfrom a sum of each fuel volume acting to generate the torque; and thetotal fuel volume of the combustion cycle is taken into account fordetermining the fuel mass that is to be injected or that has beeninjected.
 2. The method according to claim 1, wherein a fuel volume of apartial injection is determined, based on at least an actuation time ofthe pertinent final controlling element, and on the pressure acting onthe fuel.
 3. The method according to claim 1, wherein a fuel volume of apartial injection is determined based on at least an actuation time ofthe pertinent final controlling element and a variable characterizingthe actuation start.
 4. The method according to claim 2, wherein a totalfuel volume of a combustion cycle is determined from the sum of the fuelvolume of all partial injections.
 5. The method according to claim 3,wherein a fuel mass is determined from the total fuel volume, using afuel density (rho).
 6. The method according to claim 4, wherein the fuelmass is linked to a wave correction mass to yield a corrected fuel mass.7. The method according to claim 5, wherein a torque of the internalcombustion engine is determined (21) on the basis of at least thecorrected fuel mass and a rotational speed (n) of the internalcombustion engine.
 8. The method according to claim 6, wherein thedetermined torque of the internal combustion engine is linked to anefficiency correction factor to yield a corrected torque of the internalcombustion engine.
 9. The method according to claim 6, wherein the wavecorrection mass is determined on the basis of at least the fuel volumeof the partial injections and of the pressure acting on the fuel. 10.The method according to claim 1, wherein the error response is initiatedwhen the actual torque is greater than the permitted torque.
 11. Themethod according to claim 2, wherein the determined fuel volume iscorrected as a function of the start of actuation of the correspondingfinal controlling element.
 12. The method according to claim 10, whereina correction factor for correcting is taken from an injection efficiencycharacteristic map, which is a function of the actuation start.
 13. Themethod according to claim 1 for monitoring a direct injection dieselengine.